This invention relates generally to steering of automotive vehicles and more particularly to a method and system for controlling the rear wheel steering of a four-wheel steering system of an automotive vehicle (hereinafter referred to as vehicle).
There have been proposed and developed four-wheel steering systems of vehicles of the type where a reference value of the rear-wheel steering angle is determined from the steering angle of the steering wheel and the vehicle speed. And in accordance with this reference value, the rear wheels are steered. In these four-wheel steering systems, means for detecting the angular speed of the steering wheel is provided. And in accordance with the angular speed, a reference value of the rear-wheel steering speed is determined. Then, by steering at the speed of this reference value, rear-wheel steering without response delay can be realized. One example of these steering systems is disclosed in Japanese patent Laid-Open Publication No. 149562/1987.
It has been well known that, when the front wheels are steered at exceeding predetermined speed in a turn, steering the rear wheels in the same direction as that of the front wheels (so-called "coincident-phase steering") improves the stability of the vehicle. In a four-wheel steering system, this stability is improved by the front/rear-wheel coincident-phase steering for high-speed driving. However, if the rear wheel steering speed is controlled in proportion to the steering wheel angular speed in the four-wheel steering system like the prior art so as to decrease the response delay of the rear wheel control, there arises the problem that steering sensitivity deteriorates in the front/rear-wheel coincident-phase steering during steering at medium or high speed driving (i.e, sluggishness of variation of the vehicle orientation relative to the steering action) arises. The driver feels uncomfortable.